The reuptake of choline produced by hydrolysis of acetylcholine is necessary for cholinergic function and is thought to be associated specifically with cholinergic terminals and the synthesis of acetylcholine (ACh). Glial cells may modulate synaptic function by participating in the reuptake process for neuronally released transmitters and choline. We propose to more clearly define specificity of choline uptake, and its modulation by glia by the use of several cell lines used as models of normal function. C6 astrocytoma and several clones of neuroblastoma will be used as models of glia and neurons respectively. We have found that the C6 and NB 41 lines and the RN 22 Schwannoma line all possess a high-affinity carrier-mediated transport system for choline with Km about 8 micron M. A striking difference between the neuronal and glial lines has been observed in that the neuronal transport of choline is depressed in the absence of sodium whereas the glial transport of choline is increased 3-6 fold in the absence of sodium. Experiments are in progress to determine the physiological basis of this difference and to decide whether it is related to the role of glia in the modulation of the cationic environment around neurons. The synthesis of ACh, as related to choline uptake, will be examined further by chromatographic identification of products and by direct measurement of ACh and choline in the culture material to determine the role of choline uptake in the regulation of ACh synthesis and vice versa.